Proton conductivity of acid-functionalized zeolite beta, MCM-41, and MCM-48 : effect of acid strength

Abstract

Direct methanol fuel cells (DMFCs) and hydrogen proton exchange membrane fuel cells (PEMFCs) are two types of fuel cells where commercial products have been developed, but have yet to find widespread deployment. Although these devices are compact, easily refuelable, and operate at comparatively low temperatures, problems such as catalyst poisoning, methanol crossover, and water management exist and are current topics of research. One important component of both the DMFC and PEMFC is a protonically conducting but electronically insulating membrane placed between the anode and cathode. To minimize internal ohmic losses, the membrane must possess a high proton conductivity, and is commonly formed from Nafion or other perfluorosulfonic acid polymers. When fully hydrated, these polymers exhibit proton conductivites on the order of 1 × 10^(-1) to 1 × 10^(−2) S/cm. For hydrogen PEMFC without active humidification, proton conductivity decreases rapidly with increasing temperaure. For DMFC, membrane swelling allows methanol diffusion directly from anode to cathode decreasing cell efficiency.

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